Adhesive sheet and method for producing adhesive sheet

ABSTRACT

The present invention relates to a pressure sensitive adhesive sheet containing, laminated in this order, a supporting substrate, a pressure sensitive adhesive layer (X), a continuous void-containing layer including a composition containing silica particles, and a pressure sensitive adhesive layer (Y), the continuous void-containing layer having a mass concentration of the silica particles of more than 60% and 100% or less.

TECHNICAL FIELD

The present invention relates to a pressure sensitive adhesive sheet,and more specifically, relates to a blister resistant pressure sensitiveadhesive sheet that, on attaching to a surface of various plastic moldedarticles, is suppressed in occurrence of blister, including lifting.

BACKGROUND ART

A pressure sensitive adhesive sheet containing a supporting substratehaving coated thereon a pressure sensitive adhesive has been widely usedin many fields due to the convenience thereof that the sheet can beeasily attached to an adherend by pressing. In recent years, plasticmolded articles are being used frequently corresponding to the demands,such as weight saving of products. Associated thereto, there is anincreasing use of a pressure sensitive adhesive sheet for attaching to aplastic molded article. Examples of the plastic molded articles includethose obtained by molding a resin, such as polycarbonate, polymethylmethacrylate, polystyrene, and ABS.

In the case where a pressure sensitive adhesive sheet (such as apressure sensitive adhesive label) using a supporting substrate havinggas barrier property is attached to the surface of the plastic moldedarticle for such a purpose as decoration, there are cases where a gas isgenerated from the plastic molded article to form bubbles between thepressure sensitive adhesive sheet and the plastic molded article, whichcauses blister including lifting. The occurrence of blister impairs theappearance of the label, and the decorative function of the pressuresensitive adhesive sheet is significantly deteriorated.

For solving the problem, for example, PTL 1 describes, as a pressuresensitive adhesive composition, an acrylic pressure sensitive adhesivecomposition containing a copolymer obtained by radical polymerization ofa (meth)acrylate ester, a copolymerizable carboxyl group-containingcompound, and a tertiary amine having a vinyl group.

PTL 2 proposes a blister resistant pressure sensitive adhesive sheetusing a pressure sensitive adhesive containing a copolymer containing anacrylate ester having an alkyl group having from 4 to 12 carbon atomsand from 0.1 to 10% by weight of a polar monomer, such as acrylic acidand 2-hydroxyethyl acrylate, to which an aziridine cross-linking agentis added.

PTL 3 describes a pressure sensitive adhesive sheet containing, ascomponents forming a pressure sensitive adhesive layer, a pressuresensitive adhesive component and a curing component, which is an acrylicmonomer or oligomer, but there are cases where the curing componentimpairs the cohesive strength of the pressure sensitive adhesive layer,and in the case where the curing component has poor compatibility withthe pressure sensitive adhesive component, the pressure sensitiveadhesive layer becomes cloudy.

PTL 4 describes a pressure sensitive adhesive composition containing aresin composition obtained by copolymerizing an alkyl (meth)acrylatehaving from 1 to 12 carbon atoms and a carboxyl group-containingunsaturated monomer, having the particular molecular weight, and a resincomposition obtained by copolymerizing one kind or two or more kinds ofa monomer selected from an alkyl methacrylate or cycloalkyl methacrylatehaving from 1 to 20 carbon atoms, benzyl methacrylate, and styrene, withan amino group-containing unsaturated monomer, having the particularglass transition temperature (Tg) and the particular molecular weight.

PTL 5 describes a blister resistant pressure sensitive adhesivecomposition containing a copolymer obtained by copolymerizing an alkyl(meth)acrylate having an alkyl group having from 1 to 12 carbon atoms asa major component, a styrene monomer, a carboxyl group-containingunsaturated monomer, and an amino group-containing unsaturated monomer,having the particular molecular weight, with which a cross-linking agenthaving a glycidyl group is mixed.

PTL 6 describes a resin composition obtained through polymerization inacetone, having a weight average molecular weight of 1,500,000 or moreand a ratio (weight average molecular weight)/(number average molecularweight) of 4.0 or less.

CITATION LIST Patent Literatures

-   PTL 1: JP-A-2-3481-   PTL 2: JP-A-8-3521-   PTL 3: JP-A-10-279900-   PTL 4: JP-A-10-310754-   PTL 5: JP-A-2001-335766-   PTL 6: JP-A-2001-354745

SUMMARY OF INVENTION Technical Problem

However, all the techniques described in PTLs 1 to 6 have problems thatthe composition, the species of the cross-linking agent, the molecularweight, and the like of the pressure sensitive adhesive are limited, theapplicable pressure sensitive adhesive is limited, and it is difficultto achieve simultaneously both the pressure sensitive characteristicsand the blister resistance, which are necessary for the purpose oflabels.

Under the circumstances, an object of the present invention is toprovide a pressure sensitive adhesive sheet that, on attaching to asurface of various plastic molded articles, is suppressed in occurrenceof blister, including lifting, even after the lapse of time, exhibitsexcellent blister resistance with any type of the pressure sensitiveadhesive, and can be produced easily.

Solution to Problem

As a result of earnest investigations for solving the problem, thepresent inventors have found that the problems can be solved by apressure sensitive adhesive sheet containing, laminated in this order, asupporting substrate, a pressure sensitive adhesive layer, a continuousvoid-containing layer containing a composition containing silicaparticles, and a pressure sensitive adhesive layer, in which the massconcentration of the silica particles in the continuous void-containinglayer is in a particular range. The present invention has been completedbased on the knowledge.

Accordingly, the present invention provides:

(1) a pressure sensitive adhesive sheet containing, laminated in thisorder, a supporting substrate, a pressure sensitive adhesive layer (X),a continuous void-containing layer including a composition containingsilica particles, and a pressure sensitive adhesive layer (Y), thecontinuous void-containing layer having a mass concentration of thesilica particles of more than 60% and 100% or less,

(2) the pressure sensitive adhesive sheet according to the item (1),wherein the continuous void-containing layer has a thickness incrementalrate by voids of more than 170% and 280% or less,

(3) the pressure sensitive adhesive sheet according to the item (1) or(2), wherein the silica particles as a material forming the continuousvoid-containing layer have a volume average secondary particle diameterof from 0.5 to 10 μm,

(4) a method for producing the pressure sensitive adhesive sheetaccording to any one of the items (1) to (3) containing, laminated inthis order, a supporting substrate, a pressure sensitive adhesive layer(X), a continuous void-containing layer, and a pressure sensitiveadhesive layer (Y), the method containing simultaneously coating atleast two layers of the pressure sensitive adhesive layer (X), thecontinuous void-containing layer, and the pressure sensitive adhesivelayer (Y), with a multilayer coater, and

(5) a method for producing the pressure sensitive adhesive sheetaccording to any one of the items (1) to (3) containing, laminated inthis order, a supporting substrate, a pressure sensitive adhesive layer(X), a continuous void-containing layer, and a pressure sensitiveadhesive layer (Y), the method containing laminating each of thepressure sensitive adhesive layer (X), the continuous void-containinglayer, and the pressure sensitive adhesive layer (Y), by bonding.

Advantageous Effects of Invention

The pressure sensitive adhesive sheet of the present invention has alayer structure containing, laminated in this order, a supportingsubstrate, a pressure sensitive adhesive layer (X), a continuousvoid-containing layer containing a particular proportion of silicaparticles, and a pressure sensitive adhesive layer (Y), and thus such apressure sensitive adhesive sheet can be provided that exhibitsexcellent blister resistance with any type of the pressure sensitiveadhesive, and can be produced easily.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross sectional view showing an example of thestructure of the pressure sensitive adhesive sheet of the presentinvention.

FIG. 2 is an electron micrograph of the continuous void-containing layerformed in Example 1 (mass concentration of silica particles: 61%), inwhich (a) shows the surface image, and (b) shows the cross sectionalimage.

FIG. 3 is an electron micrograph of the layer formed in ComparativeExample 2 (mass concentration of silica particles: 22.3%), in which (a)shows the surface image, and (b) shows the cross sectional image.

DESCRIPTION OF EMBODIMENTS

The pressure sensitive adhesive sheet of the present invention will bedescribed.

The pressure sensitive adhesive sheet of the present invention contains,laminated in this order, a supporting substrate, a pressure sensitiveadhesive layer (X), a continuous void-containing layer including acomposition containing silica particles, and a pressure sensitiveadhesive layer (Y), and the continuous void-containing layer has a massconcentration of the silica particles of more than 60% and 100% or less.

It suffices that the pressure sensitive adhesive sheet of the presentinvention contains the pressure sensitive adhesive layer (X), thecontinuous void-containing layer, and the pressure sensitive adhesivelayer (Y) that are laminated in this order, and a layer containing thecomponents constituting the layers mixed with each other at theinterface between the layers (which may be hereinafter referred to as a“mixed layer”) may be formed.

Examples of the mixed layer include a layer containing the componentsconstituting two layers of the pressure sensitive adhesive layer (X) andthe continuous void-containing layer mixed with each other, a layercontaining the components constituting two layers of the continuousvoid-containing layer and the pressure sensitive adhesive layer (Y)mixed with each other, and a layer containing the componentsconstituting three layers of the pressure sensitive adhesive layer (X),the continuous void-containing layer, and the pressure sensitiveadhesive layer (Y) mixed with each other. Examples of the method forforming the mixed layer include a method of forming the pressuresensitive adhesive layer (X) or the continuous void-containing layer,and then forming the continuous void-containing layer or the pressuresensitive adhesive layer (Y) as an upper layer thereof by a so-calledwet-on-wet or wet-on-dry process.

Supporting Substrate

The supporting substrate used in the pressure sensitive adhesive sheetof the present invention is not particularly limited, and varioussubstrates that have been used as a supporting substrate of a pressuresensitive adhesive sheet may be used. Examples of the supportingsubstrate include a plastic film, for example, a polyester film, such asa polyethylene terephthalate film, a polybutylene terephthalate film,and a polyethylene naphthalate film, a polyethylene film, apolypropylene film, a polyvinyl chloride film, a polyvinylidene chloridefilm, a polyvinyl alcohol film, an ethylene-vinyl acetate copolymerfilm, a polystyrene film, a polycarbonate film, a polymethylpentenefilm, a polysulfone film, a polyether ether ketone film, a polyethersulfone film, a polyphenylene sulfide film, a polyether imide film, apolyimide film, a fluorine resin film, a polyamide film, an acrylicresin film, a norbornene resin film, and a cycloolefin resin film.

Among these, a polyethylene terephthalate film is preferred. For apurpose that requires heat resistance or the like, a polyethylenenaphthalate film, a polyimide film, and a polyether imide film, whichhave a high glass transition temperature (Tg), may be used. For apurpose that requires weather resistance or the like, a polyvinylchloride film, a polyvinylidene chloride film, a fluorine resin film,and an acrylic resin film, which have weather resistance, may be used.

The thickness of the plastic film is not particularly limited, and isgenerally approximately from 5 to 200 μm, preferably from 25 to 120 μm,more preferably from 30 to 90 μm, and further preferably from 40 to 60μm.

Metal Layer

The supporting substrate in the present invention is preferably a gasimpermeable substrate, with which the suppression of blister, i.e., theadvantageous effect of the present invention, can be more clearlyexhibited.

The gas impermeable substrate used may be a substrate containing theaforementioned plastic film having thereon a metal layer. Examples ofthe method for forming the metal layer include a method ofvapor-depositing a metal having metallic luster, specifically aluminum,tin, chromium, titanium, and the like, by a PVD method, such as vacuumvapor deposition, sputtering, and ion plating, and a method of bonding ametal foil having metallic luster, specifically an aluminum foil, a tinfoil, a chromium foil, a titanium foil, and the like, through variouskinds of a pressure sensitive adhesive layer generally used. Inparticular, the method of vapor-depositing a metal having metallicluster is advantageous from the standpoint of the appearance of theresulting pressure sensitive adhesive sheet and the economic efficiency.

The plastic film may be subjected to a surface treatment by an oxidationmethod, a roughening method, or the like, or a primer treatment,depending on necessity, for the purpose of the enhancement of theadhesiveness to the layer provided on the surface thereof. Examples ofthe oxidation method include a corona discharge treatment, a plasmadischarge treatment, a chromic acid treatment (wet treatment), a hot airtreatment, and an ozone or ultraviolet ray irradiation treatment, andexamples of the roughening treatment include a sand blasting treatmentand a solvent treatment. The surface treatment method may beappropriately selected corresponding to the kind of the plastic film,and a corona discharge treatment is generally preferably used from thestandpoint of the effect, the handleability, and the like.

Continuous Void-Containing Layer

The continuous void-containing layer (which may be hereinafter referredsimply to as a void-containing layer) constituting the pressuresensitive adhesive sheet of the present invention is a layer containinga composition containing silica particles, and the mass concentration ofthe silica particles in the void-containing layer is necessarily morethan 60% and 100% or less, preferably from 61 to 93%, more preferablyfrom 63 to 88%, further preferably from 66 to 83%, and still furtherpreferably from 68 to 78%. When the mass concentration of the silicaparticles is in the range, the occurrence of blister can be suppressed,and the pressure sensitive adhesive sheet can be stably produced.

The mass concentration of the silica particles in the void-containinglayer can be calculated by the following expression (2). The total massof the continuous void-containing layer means the total mass of thetotal solid content of the coating liquid for a continuousvoid-containing layer used for forming the continuous void-containinglayer.mass concentration of silica particles=(mass of silica particles/totalmass of continuous void-containing layer)×100  (2)Thickness Incremental Rate by Voids

The thickness incremental rate of the void-containing layer by voids ispreferably more than 170% and 280% or less, more preferably from 180 to270%, further preferably from 195 to 260%, still further preferably from205 to 250%, and still further preferably from 220 to 245%.

The thickness incremental rate of the void-containing layer by voidsthat is in the range may facilitate the escape of the gas generated fromthe plastic molded article or the like, and thereby the pressuresensitive adhesive sheet may have excellent blister resistance.

Calculation Method of Thickness Incremental Rate by Voids

The thickness incremental rate of the void-containing layer by voids canbe calculated by the following manner.

The film thickness in the case where no void is contained is calculatedby dividing the measured value of the coated amount by the specificgravity of the dried coated film (underlined part), and then themeasured film thickness is divided by the film thickness in the casewhere no void is contained according to the following expression (1),thereby calculating the thickness incremental rate by voids.thickness incremental rate by voids (%)=measured filmthickness×100/(measured value of coated amount)/(specific gravity ofdried coated film)  (1)

The measured film thickness is the value obtained by measuring thethickness of the void-containing layer with a constant pressurethickness gauge (PG-02, a product name, produced by Teclock Corporation)according to JIS K7130. The coated amount is the dry mass of thevoid-containing layer per unit area. The specific gravity of the driedcoated film is the value calculated from the mass fractions of thespecific gravity of the materials.

Voids

The silica particles as a material forming the continuousvoid-containing layer are actually constituted by primary particlesand/or secondary particles. The voids in the continuous void-containinglayer include voids present among the primary particles of the silicaparticles and voids present inside the secondary particles, and as forthe secondary particles, the voids include not only voids present amongthe secondary particles, but also voids present inside the secondaryparticles. Therefore, the continuous void-containing layer has such aregion that the void present among the secondary particles and the voidpresent inside the secondary particles are connected to each other toform a cavity (fine pore), and also has such a region that the voidpresent among the primary particles and the void present among thesecondary particles and/or the void present inside the secondaryparticles are connected to each other to form a cavity (fine pore).These continuous voids form voids that are continuous in the thicknessdirection, thereby ensuring sufficient gas escaping paths, which preventblister from occurring.

Silica Particles

The silica particles as a material forming the void-containing layer mayhave a spherical shape or may be a pulverization type. The silicaparticles may be any of dry silica, wet silica, and organic modifiedsilica, and may be a mixture of two or more thereof.

The mass concentration of silica in the silica particles is preferablyfrom 70 to 100% by mass, more preferably from 85 to 100% by mass, andfurther preferably from 90 to 100% by mass. The volume average secondaryparticle diameter of the silica particles as a material forming thevoid-containing layer is preferably from 0.5 to 10 μm, more preferablyfrom 1 to 8 μm, and further preferably from 1.5 to 5 μm. The volumeaverage secondary particle diameter of the silica particles can beobtained by measuring the particle size distribution with Multisizer III(produced by Beckman Coulter Inc.) or the like by the Coulter Countermethod.

The void-containing layer may contain, in addition to the silicaparticles, other inorganic particles, such as titanium oxide, bariumsulfate, alumina, calcium carbonate, magnesium carbonate, and glassbeads, and organic particles, such as acrylic beads, in such a rangethat does not impair the objects of the present invention.

Pressure Sensitive Adhesive

The continuous void-containing layer preferably contains a pressuresensitive adhesive as a component thereof, from the standpoint of theadhesiveness between the continuous void-containing layer and thepressure sensitive adhesive layer, and the standpoint that a substancehaving pressure sensitive adhesiveness tends to provide a largeradhesion force to an adherend as a result of the bulk influence thereofas compared to a substance having no pressure sensitive adhesivenesswith the same thickness.

The pressure sensitive adhesive constituting the continuousvoid-containing layer is not particularly limited, and while variouspressure sensitive adhesives, such as a rubber pressure sensitiveadhesive, a silicone pressure sensitive adhesive, and an acrylicpressure sensitive adhesive, may be used, an acrylic pressure sensitiveadhesive is preferred from the standpoint of the capability as apressure sensitive adhesive, the weather resistance, and the like. Thepressure sensitive adhesive may be any of a solvent type and an emulsiontype. The solvent type pressure sensitive adhesive may contain across-linking agent depending on necessity.

Examples of the material constituting the acrylic pressure sensitiveadhesive include a (co)polymer having a constitutional unit derived froman alkyl (meth)acrylate having a linear or branched alkyl group and a(co)polymer having a constitutional unit derived from a (meth)acrylatehaving a cyclic structure.

The (meth)acrylate means one or more selected from an acrylate and amethacrylate, and the (co)polymer means one or more selected from apolymer and a copolymer.

The acrylic pressure sensitive adhesive preferably contains as apressure sensitive adhesive component a (meth)acrylate ester (co)polymerhaving a weight average molecular weight of from 100,000 to 1,500,000and a cross-linking agent, and from the standpoint of the void ratio,the shear storage elastic modulus at 100° C. of the cross-linkedpressure sensitive adhesive is preferably 9.0×10³ Pa or more, morepreferably 1.0×10⁴ Pa or more, and further preferably 2.0×10⁴ Pa ormore. When the shear storage elastic modulus is 9.0×10³ Pa or more, thevoids can be retained to provide excellent blister resistance.

The shear storage elastic modulus can be obtained by measuring with aviscoelasticity measuring instrument (Dynamic Analyzer RDA II, a productname, produced by Rheometrics, Inc.) at a frequency of 1 Hz.

The pressure sensitive adhesive constituting the continuousvoid-containing layer and that used in the pressure sensitive adhesivelayer described later are preferably the same as each other from thestandpoint of the adhesiveness between the continuous void-containinglayer and the pressure sensitive adhesive layer.

Examples of the cross-linking agent include a polyisocyanate compound,an epoxy resin, a melamine resin, a urea resin, a dialdehyde compound, amethylol polymer, an aziridine compound, a metal alkoxide, and a metalsalt, and a polyisocyanate compound is preferably used. Thecross-linking agent may be mixed in an amount of preferably from 0 to 30parts by mass, more preferably from 0.01 to 15 parts by mass, furtherpreferably from 0.5 to 10 parts by mass, and still further preferablyfrom 2 to 7 parts by mass, per 100 parts by mass of the solid content ofthe (meth)acrylate ester (co)polymer.

Examples of the polyisocyanate compound include an aromaticpolyisocyanate, such as tolylene diisocyanate, diphenylmethanediisocyanate, and xylylene diisocyanate, an aliphatic polyisocyanate,such as hexamethylene diisocyanate, an alicyclic polyisocyanate, such asisophorone diisocyanate and hydrogenated diphenylmethane diisocyanate,and a biuret thereof, an isocyanurate thereof, and an adduct thereof,which is a reaction product thereof with a low molecular weight activehydrogen-containing compound, such as ethylene glycol, propylene glycol,neopentyl glycol, trimethylolpropane, and castor oil. The cross-linkingagent may be used solely or as a combination of two or more kindsthereof.

The acrylic pressure sensitive adhesive used in the present inventionmay contain a general additive in such a range that does not impair theadvantageous effects of the present invention.

Examples of the general additive include a tackifier, an antioxidant, asoftener (plasticizer), a filler, a rust preventing agent, a pigment, adye, a retardant, a reaction accelerator, and an ultraviolet rayabsorbent.

In the case where the general additive is contained, the content of eachof the general additives is preferably from 0.0001 to 60 parts by mass,and more preferably from 0.001 to 50 parts by mass, per 100 parts bymass of the solid content of the pressure sensitive adhesive.

The thickness of the continuous void-containing layer is preferably from5 to 100 μm, more preferably from 7 to 50 μm, further preferably from 10to 30 μm, and still further preferably from 15 to 25 μm. When thethickness of the continuous void-containing layer is 5 μm or more, athickness that is sufficient for embedding the silica particles can beensured to form the continuous void-containing layer having lessunevenness, and the blister resistance can be ensured. When thethickness of the continuous void-containing layer is 100 μm or less, theamount of the silica particles used can be suppressed, which iseconomically preferred.

The continuous void-containing layer may be formed by coating a coatingliquid for the continuous void-containing layer containing the silicaparticles and the pressure sensitive adhesive, which is used dependingon necessity.

Pressure Sensitive Adhesive Layers (X) and (Y)

FIG. 1 is a schematic cross sectional view showing an example of thestructure of the pressure sensitive adhesive sheet of the presentinvention, and as shown in FIG. 1, the pressure sensitive adhesive sheet10 of the present invention has a structure containing a supportingsubstrate 1 having a metal layer 2 on the surface thereof, havinglaminated in this order on the metal layer 2 a pressure sensitiveadhesive layer (X) 3, the continuous void-containing layer 4, a pressuresensitive adhesive layer (Y) 5, and a release sheet 6.

In the pressure sensitive adhesive sheet of the present invention, thepressure sensitive adhesive constituting the pressure sensitive adhesivelayer (X) and the pressure sensitive adhesive layer (Y) is notparticularly limited since the pressure sensitive adhesive layers maynot necessarily have a blister resistant function by themselves, andwhile various pressure sensitive adhesives, such as a rubber pressuresensitive adhesive, a silicone pressure sensitive adhesive, and anacrylic pressure sensitive adhesive, may be used, an acrylic pressuresensitive adhesive is preferred from the standpoint of the capability asa pressure sensitive adhesive, the weather resistance, and the like. Thepressure sensitive adhesive may be any of a solvent type and an emulsiontype. A cross-linking agent may be contained depending on necessity.

The thickness of the pressure sensitive adhesive layer (X) and thepressure sensitive adhesive layer (Y) in the pressure sensitive adhesivesheet of the present invention is preferably from 5 to 50 μm, morepreferably from 7 to 35 μm, and further preferably from 10 to 30 μm.

The ratio of the thickness of the pressure sensitive adhesive layer (X)and the continuous void-containing layer (pressure sensitive adhesivelayer (X)/continuous void-containing layer) is preferably from 0.05 to10, more preferably from 0.1 to 5, further preferably from 0.2 to 2, andstill further preferably from 0.3 to 0.8, from the standpoint of theachievement of both the excellent appearance and the blister resistance.

The ratio of the thickness of the pressure sensitive adhesive layer (Y)and the continuous void-containing layer (pressure sensitive adhesivelayer (Y)/continuous void-containing layer) is preferably from 0.05 to10, more preferably from 0.1 to 5, further preferably from 0.2 to 2, andstill further preferably from 0.3 to 0.8, from the standpoint of theachievement of both the excellent appearance and the blister resistance.

The two pressure sensitive adhesive layers (X) and (Y) may have the samecomposition or different compositions. The compositions of the pressuresensitive adhesive layers are not particularly limited, and the samepressure sensitive adhesive as that used in the continuousvoid-containing layer may be used therefor.

The method for producing a pressure sensitive adhesive sheet of thepresent invention will be described.

Method I for Producing Pressure Sensitive Adhesive Sheet

The method for producing a pressure sensitive adhesive sheet of thepresent invention is a method for producing a pressure sensitiveadhesive sheet containing, laminated in this order, a supportingsubstrate, a pressure sensitive adhesive layer (X), a continuousvoid-containing layer, and a pressure sensitive adhesive layer (Y), andthe method contains simultaneously coating at least two layers of thepressure sensitive adhesive layer (X), the continuous void-containinglayer, and the pressure sensitive adhesive layer (Y), with a multilayercoater.

The layers to be simultaneously coated are at least two layers of thepressure sensitive adhesive layer (X), the continuous void-containinglayer, and the pressure sensitive adhesive layer (Y) from the standpointof the productivity, and it is preferred that the three layers, i.e.,the pressure sensitive adhesive layer (X), the continuousvoid-containing layer, and the pressure sensitive adhesive layer (Y) aresimultaneously coated.

In the simultaneous coating, the layers may be coated directly on thesupporting substrate, or may be coated on a release-treated surface of arelease sheet described later for protecting the pressure sensitiveadhesive layers.

Examples of the coater as the multilayer coater for simultaneous coatingin the production method I include a curtain coater and a die coater,and among these, a die coater is preferably used from the standpoint ofthe operationality.

Method II for Producing Pressure Sensitive Adhesive Sheet

The method II for producing a pressure sensitive adhesive sheet of thepresent invention is a method for producing a pressure sensitiveadhesive sheet containing, laminated in this order, a supportingsubstrate, a pressure sensitive adhesive layer (X), a continuousvoid-containing layer, and a pressure sensitive adhesive layer (Y), andthe method contains laminating each of the pressure sensitive adhesivelayer (X), the continuous void-containing layer, and the pressuresensitive adhesive layer (Y), by bonding.

Examples of the method of laminating by bonding in the production methodII include such a method that the prescribed pressure sensitive adhesiveis coated on a release-treated surface of a release sheet to a thicknessafter drying of preferably from 5 to 50 μm, more preferably from 7 to 35μm, and further preferably from 10 to 30 μm, followed by drying, by aknown method, so as to produce a pressure sensitive adhesive sheethaving the release sheet, which is then adhered to the continuousvoid-containing layer by using a lamination roll.

Examples of the coater used for forming and coating the layers in theproduction method II include an air knife coater, a blade coater, a barcoater, a gravure coater, a roll coater, a roll knife coater, a curtaincoater, a the coater, a knife coater, a screen coater, a Meyer barcoater, and a kiss coater, and among these, a roll knife coater and adie coater are preferred from the standpoint of the operationality.After forming and coating the layers, the layers are dried. The dryingtemperature is preferably from 35 to 200° C.

The following production method may also be used, i.e., a method forproducing a pressure sensitive adhesive sheet containing, laminated inthis order, a supporting substrate, a pressure sensitive adhesive layer(X), a continuous void-containing layer, and a pressure sensitiveadhesive layer (Y), and the method contains laminating at least twolayers of the pressure sensitive adhesive layer (X), the continuousvoid-containing layer, and the pressure sensitive adhesive layer (Y), bya so-called wet-on-wet or wet-on-dry process, which is not multilayersimultaneous coating.

The wet-on-wet process is, for example, a method of coating a coatingliquid for forming the pressure sensitive adhesive layer (X), andwithout drying, further coating thereon a coating liquid for forming thecontinuous void-containing layer.

The wet-on-dry process is, for example, a method of coating a coatingliquid for forming the pressure sensitive adhesive layer (X), coatingthereon a coating liquid for forming the continuous void-containinglayer, and then after drying, coating a coating liquid for forming thepressure sensitive adhesive layer (Y).

Such a method may also be used that a pressure sensitive adhesive sheethaving laminated in this order the pressure sensitive adhesive layer(X), the continuous void-containing layer, and the pressure sensitiveadhesive layer (Y), without a substrate is produced, and then thesupporting substrate is laminated thereon. In this case, the pressuresensitive adhesive sheet without substrate may have a release sheetdescribed later for protecting the pressure sensitive adhesive layers.

Release Sheet

Examples of the release sheet used in the method for producing apressure sensitive adhesive sheet described above include a releasesheet containing a film formed of various resins, such as polyethyleneterephthalate, polybutylene terephthalate, polyethylene, polypropylene,and polyacrylate, or a paper material, such as polyethylene laminatedpaper, polypropylene laminated paper, clay coated paper, resin coatedpaper, glassine paper, and wood-free paper, as a substrate, in which thebonding surface of the substrate to the pressure sensitive adhesivelayer is subjected to a release treatment depending on necessity.

Examples of the release treatment include formation of a release agentlayer formed of a release agent, such as a silicone resin, a long-chainalkyl resin, and a fluorine resin. The thickness of the release sheet isnot particularly limited, and is generally from 20 to 200 μm, preferablyfrom 25 to 180 μm, and more preferably from 35 to 170 μm.

The pressure sensitive adhesive sheet of the invention thus produced maybe attached to a plastic molded article, such as polycarbonate,polymethyl methacrylate, polystyrene, and an ABS resin, and effectivelyprevent blister from occurring.

EXAMPLES

The present invention will be described in more detail with reference toexamples, but the present invention is not limited to the examples inany way.

The blister resistance of the pressure sensitive adhesive sheetsobtained in the examples was evaluated by the following method.

Evaluation of Blister Resistance

The pressure sensitive adhesive sheet of 50 mm×50 mm, from which therelease sheet had been removed, was attached to a polymethylmethacrylate plate (“Acrylite L001”, produced by Mitsubishi Rayon Co.,Ltd.), a polycarbonate plate (“Iupilon Sheet NF-2000UV”, produced byMitsubishi Gas Chemical Co., Inc.), and a polystyrene plate (“Dialite201B W1001”, produced by Kyoei Jushi Corporation) each of 70 mm×150 mmhaving a thickness of 2 mm under pressure with a squeegee, which wereallowed to stand at 23° C. for 12 hours, then allowed to stand in a hotair dryer at 80° C. for 1.5 hours, and then allowed to stand in a hotair dryer at 90° C. for 1.5 hours, and the occurrence status of blisterafter the heat acceleration was observed and evaluated under thefollowing standard.

A: No blister was observed visually.

B: Blister was partially observed visually.

C: Blister was observed visually over the entire surface.

Measurement of Volume Average Secondary Particle Diameter of SilicaParticles

The volume average secondary particle diameter of the silica particlesas a material forming the continuous void-containing layer was obtainedby measuring the particle size distribution with Multisizer III(produced by Beckman Coulter Inc.) or the like by the Coulter Countermethod.

Measurement of Thickness Incremental Rate and Mass Concentration ofSilica Particles

The thickness incremental rate by voids in the continuousvoid-containing layer and the mass concentration of the silica particleswere calculated by the expressions (1) and (2) described hereinabove,respectively.

Measurement of Film Thickness

The film thickness was obtained by measuring the thickness of thevoid-containing layer with a constant pressure thickness gauge (“PG-02”,a product name, produced by Teclock Corporation) according to JIS K7130.

Example 1

Preparation of Coating Liquid (A) for Forming Pressure SensitiveAdhesive Layer

To 100 parts by mass of an acrylic resin solution (an acrylic copolymercontaining butyl acrylate (hereinafter referred to as “BA”) and acrylicacid (hereinafter referred to as “AA”) (mass concentration ratio of BAand AA (BA/AA)=90/10 (% by mass)), weight average molecular weight (Mw):470,000, solid concentration: 33.6% by mass, solvent: mixed solvent oftoluene and ethyl acetate), 1 part by mass of an isocyanatecross-linking agent (“Coronate L”, a trade name, produced by NipponPolyurethane Co., Ltd., solid concentration: 75% by mass) (2.23 parts bymass of the solid content per 100 parts by mass of the acryliccopolymer) and ethyl acetate were added, so as to provide a coatingliquid (A) for forming a pressure sensitive adhesive layer (solidconcentration: 28% by mass).

Preparation of Coating Liquid (B1) for Forming ContinuousVoid-Containing Layer

To 100 parts by mass of an acrylic resin solution (an acrylic copolymercontaining BA and AA) (mass concentration ratio of BA and AA(BA/AA)=90/10 (% by mass)), weight average molecular weight (Mw):470,000, solid concentration: 33.6% by mass, solvent: mixed solvent oftoluene and ethyl acetate), 53.67 parts by mass of silica particles(“Nipsil E-200A”, a trade name, produced by Tosoh Silica Corporation,volume average secondary particle diameter: 3 μm) and toluene wereadded, and the silica particles were dispersed in the acrylic resinsolution, so as to provide a silica-dispersed pressure sensitiveadhesive composition (solid concentration: 22% by mass). Furthermore,0.252 part by mass of an isocyanate cross-linking agent (“Coronate L”, atrade name, produced by Nippon Polyurethane Co., Ltd., solidconcentration: 75% by mass) was added to 100 parts by mass of thepressure sensitive adhesive composition (2.23 parts by mass of the solidcontent per 100 parts by mass of the acrylic copolymer), and toluene wasfurther added thereto, so as to provide a coating liquid (B1) forforming a continuous void-containing layer having a solid concentrationof 22% by mass.

Production of Pressure Sensitive Adhesive Sheet

A polyethylene terephthalate film having an aluminum vapor depositionlayer on one surface thereof (“FNS MATT N50”, a product name, producedby Lintec Corporation, thickness: 50 μm) was used as a supportingsubstrate, and release paper (“SP-11BL Ivory”, a product name, producedby Lintec Corporation, thickness: 166 μm) was used as a release sheet.On the release-treated surface of the release sheet, the coating liquid(A) for forming a pressure sensitive adhesive layer was coated to a drythickness of 10 μm with a roll coater and dried at 100° C. for 2minutes, and then bonded to the aluminum-vapor-deposited surface of thesupporting substrate with a lamination roll, so as to provide a pressuresensitive adhesive sheet (I). On the release-treated surface of therelease sheet provided separately from the above, the coating liquid(B1) for forming a continuous void-containing layer was coated to a drythickness of 20 μm with a roll coater and dried at 100° C. for 2minutes, and then bonded to the surface of the pressure sensitiveadhesive sheet (I) on the side having the dried film of the coatingliquid (A) for forming a pressure sensitive adhesive layer with alamination roll, so as to provide a pressure sensitive adhesive sheet(II). Furthermore, on the release-treated surface of the release sheetprovided separately from the above, the coating liquid (A) for forming apressure sensitive adhesive was coated to a dry thickness of 10 μm witha roll coater and dried at 100° C. for 2 minutes, and then bonded to thesurface of the pressure sensitive adhesive sheet (II) on the side havingthe dried film of the coating liquid (B1) for forming a continuousvoid-containing layer with a lamination roll, so as to provide apressure sensitive adhesive sheet of Example 1.

The continuous void-containing layer had a mass concentration of thesilica particles of 61% and a thickness incremental rate by voids of175%.

Examples 2 to 4

Coating liquids (B2) to (B4) for forming a continuous void-containinglayer were provided in the same manner as in Example 1 except that theamount of the silica particles and the amount of the isocyanatecross-linking agent in Example 1 were changed to the amounts shown inTable 1.

Subsequently, pressure sensitive adhesive sheets were produced in thesame manner as in Example 1 except that the coating liquid (B1) forforming a continuous void-containing layer in Example 1 was changed tothe coating liquids (B2) to (B4) for forming a continuousvoid-containing layer.

TABLE 1 Formulation of coating liquid (B) for continuous void-containinglayer Silica-dispersed pressure sensitive adhesive composition Coatingliquid for continuous void-containing layer Mixed amount Mixed amount(part by mass) *2 (part by mass) *1 Solid Silica-dispersed IsocyanateSolid Acrylic resin concentration pressure sensitive cross-linkingconcentration No. solution Silica particles (%) adhesive compositionagent (%) Example 1 B1 100 53.67 22 100 0.252 22 Example 2 B2 100 80.3022 100 0.193 22 Example 3 B3 100 137.83 22 100 0.128 22 Example 4 B4 100309.26 22 100 0.064 22 *1: mixed amount (part by mass) with respect to100 parts by mass of acrylic resin solution *2: mixed amount (part bymass) with respect to 100 parts by mass of silica-dispersed pressuresensitive adhesive composition

Comparative Example 1

On the release-treated surface of the release paper “SP-11BL Ivory”(described above), the coating liquid (A) for forming a pressuresensitive adhesive layer was coated with a roll coater and dried at 100°C. for 1 minute to provide a pressure sensitive adhesive layer having athickness of 40 μm, and then bonded to the aluminum-vapor-depositedsurface of the supporting substrate “FNS MATT N50” (described above witha lamination roll), so as to provide a pressure sensitive adhesivesheet.

The pressure sensitive adhesive layer of the pressure sensitive adhesivesheet had a mass concentration of silica particles of 0%.

Comparative Example 2

To 100 parts by mass of an acrylic resin solution (“Oribain BPS-4891”,produced by Toyochem Co., Ltd., solid concentration: 46% by mass), 27.6parts by mass of silica particles (“Nipsil E-200A”, a trade name,produced by Tosoh Silica Corporation, volume average secondary particlediameter: 3 μm) and a mixed solvent of toluene and MEK having a volumeratio of 1/1 were added, and the silica particles were dispersed in theacrylic resin solution, so as to provide an silica-dispersed pressuresensitive adhesive composition (solid concentration: 37% by mass).Furthermore, 1.13 parts by mass of an isocyanate cross-linking agent(“Coronate L”, a trade name, produced by Nippon Polyurethane Co., Ltd.,solid concentration: 75% by mass) was added to 100 parts by mass of thesilica-dispersed pressure sensitive adhesive composition (1.69 parts bymass of the solid content per 100 parts by mass of the acrylic resinsolution), and a mixed solvent of toluene and MEK having a volume ratioof 1/1 was further added thereto, so as to provide a silica dispersionliquid having a solid concentration of 33% by mass.

Furthermore, to 70 parts by mass of the silica dispersion liquid, 30parts by mass of an acrylic resin solution (“Oribain BPS-4891”, a tradename, produced by Toyochem Co., Ltd., solid concentration: 46% by mass)(45 parts by mass of the solid content per 100 parts by mass of theacrylic resin solution used in the silica-dispersed pressure sensitiveadhesive composition) and 1.47 parts by mass of an isocyanatecross-linking agent (“Coronate L”, a trade name, produced by NipponPolyurethane Co., Ltd., solid concentration: 75% by mass) (2.62 parts bymass of the solid content per 100 parts by mass of the acrylic resinsolution used in the silica-dispersed pressure sensitive adhesivecomposition) were added, and a mixed solvent of toluene and MEK having avolume ratio of 1/1 was further added thereto, so as to provide acoating liquid (B5) for forming a continuous void-containing layerhaving a solid concentration of 37% by mass.

A pressure sensitive adhesive sheet was produced in the same manner asin Example 1 except that the coating liquid (B5) for forming acontinuous void-containing layer was used instead of the coating liquid(B1) for forming a continuous void-containing layer.

The continuous void-containing layer had a mass concentration of thesilica particles of 22.3% and a thickness incremental rate by voids of114%.

The pressure sensitive adhesive sheets obtained in Examples andComparative Examples were evaluated for the blister resistance. Theresults are shown in Table 2 along with the mass concentration of thesilica particles in the continuous void-containing layer and thicknessincremental rate by voids.

TABLE 2 Coating liquid (B) Mass Thickness for continuous concentrationof increment void-containing silica particles rate by voids Blisterresistance *1 layer (%) (%) On PMMA On PC On PS Example 1 B1 61 175 A AA Example 2 B2 70 230 A A A Example 3 B3 80 250 A A A Example 4 B4 90263 A A A Comparative — 0 — C C C Example 1 Comparative B5 22.3 114 C CB Example 2 *1: PMMA: polymethyl methacrylate, PC: polycarbonate, PS:polystyrene

FIG. 2 shows an electron micrograph of the continuous void-containinglayer formed in Example 1 (mass concentration of silica particles: 61%),in which (a) shows the surface image, and (b) shows the cross sectionalimage.

FIG. 3 shows an electron micrograph of the layer formed in ComparativeExample 2 (mass concentration of silica particles: 22.3%), in which (a)shows the surface image, and (b) shows the cross sectional image.

In FIG. 2, the surface of the surface image (a) means the dry freesurface, but not on the side of the release sheet.

In Example 1, continuous voids are formed, whereas in ComparativeExample 2 (mass concentration of silica particles: 22.3%), no continuousvoid is formed.

The observation was performed by using a field-emission electronmicroscope “S-4700”, produced by Hitachi, Ltd. at an accelerationvoltage of 15 kV.

INDUSTRIAL APPLICABILITY

The pressure sensitive adhesive sheet of the present invention onattaching to a surface of various plastic molded articles is suppressedin occurrence of blister, including lifting, even after the lapse oftime, exhibits excellent blister resistance with any type of thepressure sensitive adhesive, and can be produced easily.

REFERENCE SIGNS LIST

-   1 supporting substrate-   2 metal layer-   3 pressure sensitive adhesive layer (X)-   4 continuous void-containing layer-   5 pressure sensitive adhesive layer (Y)-   6 release sheet-   10 pressure sensitive adhesive sheet

The invention claimed is:
 1. A pressure sensitive adhesive sheet,comprising: a supporting substrate comprising a plastic film and a metallayer; a pressure sensitive adhesive layer (X) formed on the supportingsubstrate; a continuous void-containing layer formed on the pressuresensitive adhesive layer (X) and including a composition containingsilica particles; and a pressure sensitive adhesive layer (Y) formed onthe continuous void-containing layer, wherein the continuousvoid-containing layer has a mass concentration of the silica particlesof more than 60% and 100% or less, and the silica particles are formingsecondary particles in the composition.
 2. The pressure sensitiveadhesive sheet according to claim 1, wherein the continuousvoid-containing layer has a thickness incremental rate by voids of morethan 170% and 280% or less.
 3. The pressure sensitive adhesive sheetaccording to claim 2, wherein the secondary particles have a volumeaverage diameter of from 0.5 to 10 μm.
 4. The pressure sensitiveadhesive sheet according to claim 1, wherein the secondary particleshave a volume average diameter of from 0.5 to 10 μm.
 5. A method forproducing the pressure sensitive adhesive sheet according to claim 1,the method comprising: simultaneously coating at least two layers of thepressure sensitive adhesive layer (X), the continuous void-containinglayer, and the pressure sensitive adhesive layer (Y), with a multilayercoater.
 6. A method for producing the pressure sensitive adhesive sheetaccording to claim 1, the method comprising: laminating each of thepressure sensitive adhesive layer (X), the continuous void-containinglayer, and the pressure sensitive adhesive layer (Y), by bonding.
 7. Thepressure sensitive adhesive sheet according to claim 1, wherein theplastic film comprises at least one selected from the group consistingof polyethylene terephthalate, polybutylene terephthalate, polyethylenenaphthalate, polyethylene, polypropylene, polyvinyl chloride,polyvinylidene chloride, polyvinyl alcohol, an ethylene-vinyl acetatecopolymer, polystyrene, polycarbonate, polymethylpentene, polysulfone,polyether ether ketone film, polyether sulfone, polyphenylene sulfide,polyether imide, polyimide, a fluorine resin, polyamide, an acrylicresin, a norbornene resin, and a cycloolefin resin.
 8. The pressuresensitive adhesive sheet according to claim 1, wherein the metal layercomprises at least one selected from the group consisting of aluminum,tin, chromium, and titanium.
 9. The pressure sensitive adhesive sheetaccording to claim 1, wherein the supporting substrate comprises aplastic film and a metal layer such that the pressure sensitive adhesivelayer (X) is formed on the metal layer of the supporting substrate. 10.The pressure sensitive adhesive sheet according to claim 1, wherein thecontinuous void-containing layer has the mass concentration of thesilica particles of 61 to 93%.
 11. The pressure sensitive adhesive sheetaccording to claim 1, wherein the continuous void-containing layer hasthe mass concentration of the silica particles of 68 to 78%.
 12. Thepressure sensitive adhesive sheet according to claim 1, wherein theplastic film has a thickness of from 5 to 200 μm.
 13. The pressuresensitive adhesive sheet according to claim 1, wherein the plastic filmhas a thickness of from 40 to 60 μm.
 14. The pressure sensitive adhesivesheet according to claim 1, further comprising: a release sheet formedon the pressure sensitive adhesive layer (Y) on a side opposite to aside on which the continuous void-containing layer is formed.
 15. Thepressure sensitive adhesive sheet according to claim 1, wherein thesecondary particles have a volume average diameter of from 1 to 8 μm.16. The pressure sensitive adhesive sheet according to claim 1, whereinthe secondary particles have a volume average diameter of from 1.5 to 5μm.
 17. The pressure sensitive adhesive sheet according to claim 1,wherein the silica particles are included in the continuousvoid-containing layer such that voids between the silica particles forma continuous void in the continuous void-containing layer.
 18. Thepressure sensitive adhesive sheet according to claim 1, wherein each ofthe pressure sensitive adhesive layer (X) and the pressure sensitiveadhesive layer (Y) has a thickness of from 5 to 50 μm.